1. Field of the Invention
The present invention relates to an apparatus and a method for outputting a signal having a plurality of temperature coefficients.
2. Description of the Related Art
In general, in designing circuits and devices, it is essential to ensure stability of temperature, supply voltage, processing variation, and so on, not only for ensuring the performance of the circuits and devices, but also for ensuring yield rates. Particularly, in designing stable circuits and devices, it is very important to ensure the stable operation of a bias circuit, which directly influences the performance of the circuits and devices.
Among other components of circuits and devices, transistors have characteristics that change depending on changes in temperature, and thus a bias circuit for compensating for the changes is required. The most noticeable changes in the characteristics of the transistors depending on changes in temperatures are threshold voltage and mobility. For a MOS transistor, its transconductance is changed if the threshold voltage and mobility are changed. Typically, the transconductance decreases as temperature increases, and thus a bias circuit for compensating for the decreased transconductance is required.
In the related art, as a method for compensating for changes in such temperature-dependent characteristics, there is a known technique of using a band gap reference circuit to generate a stable bias current or voltage. A proportional to absolute temperature (PTAT) circuit included in the band gap reference circuit has a positive temperature coefficient for absolute temperature so that bias current or voltage increases as temperature increases. In addition, a complementary to absolute temperature (CTAT) circuit included in the band gap reference circuit has a negative temperature coefficient for absolute temperature so that bias current or voltage decreases as temperature increases. By applying those positive and negative temperature coefficient circuits, temperature compensation may be achieved to a limited extent.
However, those positive and negative temperature coefficient circuits applied in the band gap reference circuit according to the related art have invariable, i.e., positive or negative temperature coefficients, they have limits to be applied to a circuit having various temperature-dependent characteristics.
That is, since circuit and devices also include passive elements such as resistors, in addition to MOS transistors, a temperature compensating circuit having variable temperature coefficients is required for compensating for minute changes in temperature-dependent characteristics of such passive elements. Moreover, since different circuit have different temperature coefficients of a bias circuit necessary for temperature compensation, an apparatus for outputting a signal having various temperature coefficients is required.